This invention relates to the management of network devices in packet-based communication networks and more particularly to link aggregation control, that is to say the configuration and control of a link aggregation media access control sub-layer of at least one device (an aggregator) which has a multiplicity of physical links to another device (xe2x80x98partnerxe2x80x99) which can be aggregated together to form a link aggregation group, such that a MAC xe2x80x98clientxe2x80x99 can treat the link aggregation group as if it were a single link. More particularly the invention concerns the provision of greater resilience, that is to say an enhanced ability to tolerate physical changes to a system of links while reducing a need to deconstruct or modify an existing aggregation.
As is well known, a packet-based data communication network generally comprises various forms of terminal equipment and intermediate devices such as switches, routers and repeaters which intercommunicate by means of links, constituting the transmission media for signals between the various devices. The links may be in physical form, such as twisted pair, coaxial cable, optical fibres and so on.
Generally, a particular link between a device and a remote partner has a bandwidth limited by the capabilities of the device (and more particularly the characteristics of a relevant port) although it is customary to ensure that a communication path including a link and the relevant ports on a device and its link partner operate according to one or other of a variety of transmission standards. It is frequently found that the traffic or expected traffic between a device and a link partner exceeds the capability of a particular link and it is therefore desirable to provide a plurality of parallel paths between the device and its partner. One manner of achieving this is known as xe2x80x98trunkingxe2x80x99. Another, which is more directly relevant to the subject matter of the present invention, is known as xe2x80x98link aggregationxe2x80x99.
Link aggregation for CSMA/CD (Ethernet) systems is described in considerable detail in IEEE Standard 802 3ad-2000 (published by the Institute of Electrical and Electronic Engineers Inc NY 10016-5997, USA, under ISBN 0-7381-2472-9 SH94845). As is explained in that Standard, link aggregation in effect specifies a method for linearly incrementing a system""s data rate by aggregating multiple physical links of the same speed into one logical link In this way bandwidth can be increased in unit multiples. Link aggregation also provides improved performance and resilience in that the failure of a single link within a link aggregation group need not cause failure from the point of view of a client.
Link aggregation control, which is also described in detail in the aforementioned Standard, enables in the absence of manual overrides an appropriate set of link aggregation groups to be automatically configured and automatically reconfigured if individual links are added to those groups. The link aggregation sub-layer may comprise a number of individual links in order to present a single MAC interface to a MAC client. In the aforementioned Standard there is a detailed description of link aggregation, particularly in relation to FIG. 43-2 which presents a block diagram of a link aggregation sub-layer and further FIGS. 43-3 to 43-19 which illustrate various state diagrams for link aggregation control.
In the aforementioned Standard, a device which can aggregate links to a remote partner is called an aggregator and is assigned a system identifier which includes a unique, globally administered individual MAC address (herein called ID) which corresponds to a MAC address assigned to one of its ports Currently the total system identifier is an 8-octet unsigned binary number of which the two most significant octets constitute the system priority, the third most significant octet is derived from the initial octet of the MAC address and the fourth to eighth octets are arranged to correspond to the second to sixth octets of the MAC address.
An automatically monitored and configured system of this general nature requires a protocol in order to standardise the manner in which information is exchanged between partner systems on a link to allow their link aggregation control entities to reach agreement on the identity of the link aggregation group to which the link belongs, to move the link to that link aggregation group and to enable transmission and reception to operate in a proper manner. The messages which are employed in the link aggregation control protocol (LACP) are known as LACPDUs (link aggregation control protocol data units) and each comprise an integral number of octets. They, are basic IEEE 802 3 frames and an example of the structure of an LACPDU is given in FIG. 43-7 of the aforementioned Standard and FIG. 4 herein Broadly, they are untagged frames which comprise a destination address, a source address, a length/type field, a sub-type field, a version number, an actor information field, an actor information length field, actor system priority, an Actor_System field, constituted by a system ID encoded as a globally administered, unicast MAC address, an actor key, an actor port priority, and actor port and an actor state followed by further information relating to the link partner and other fields not directly relevant to the present invention. The information relating to the partner includes a xe2x80x98Partner_Systemxe2x80x99 field of six octets, which is the partner""s system ID, encoded as a globally administered, unicast MAC address. The two fields of most relevance to the present invention are the xe2x80x98Actor_Systemxe2x80x99 field and the xe2x80x98Partner_Systemxe2x80x99 field. As will be apparent, such data units are distinguished by appropriate parsing from xe2x80x98ordinaryxe2x80x99 frames or data packets.
In current practice, there is no good means by which an aggregator can inform a partner that it no longer owns a system ID, for example because the ID no longer represents a MAC address relevant to the aggregation and accordingly the partner cannot presume that where a new aggregation has been made in the aggregator that an appropriate change in the partner""s configuration can be created It is the purpose of the present invention to deal with this difficulty and in general to provide greater resilience in aggregating systems.
In a specific example of the present invention an aggregator detects when it no longer has control of a system ID and informs the partner system identifying both the old (i.e. superseded) system ID and a new system ID. In a preferred form of the invention, data units (specifically the LACPDUs) are modified to provide in place of the partner""s ID the superseded system ID represented in a distinctive way, preferably in the form of a xe2x80x98locally administeredxe2x80x99 multicast address.
Further objects and features will be apparent from the following detailed description with reference to the drawings.